Liquid Crystal Display Device

ABSTRACT

In a liquid crystal display device that uses a TFT, a contact hole is formed to connect an image signal line. An organic film is formed so as to cover the image signal line, and a common electrode, which is a transparent electrode, is formed on the organic film. An interlayer insulating film is formed on the common electrode. A through hole is formed in the interlayer insulating film, and the diameter of the through hole is greater than the diameter of the contact hole.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/311,595, filed Dec. 6, 2011, the contents of which are incorporatedherein by reference.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2010-279155 filed on Dec. 15, 2010, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a display device, and moreparticularly, to a liquid crystal display device designed to preventpeeling of a film formed on an organic passivation film.

BACKGROUND OF THE INVENTION

A liquid crystal display device includes a TFT substrate in which pixelseach having a pixel electrode, a thin film transistor (TFT), and thelike are arranged in a matrix form. Further, a counter substrate isdisposed opposite to the TFT substrate, in which color filters and thelike are formed at positions corresponding to the pixel electrodes ofthe TFT substrate. A liquid crystal is interposed between the TFTsubstrate and the counter substrate. Then, the light transmittance iscontrolled by liquid crystal molecules in each pixel to form an image.

The use of liquid crystal display devices is growing in various fieldsdue to its flatness and lightweight. Small-sized liquid crystal displaydevices are widely used in mobile phones and digital still cameras(DSCs). In the liquid crystal display device, the viewing anglecharacteristics are a problem. The viewing angle is a phenomenon inwhich the brightness changes or the color changes between when thedisplay is viewed from the front and when the display is viewed from anoblique direction. The viewing angle characteristics are excellent inthe in-plane switching (IPS) mode for driving liquid crystal moleculesby the electric field in the horizontal direction.

There are many different types of IPS mode. For example, a commonelectrode is formed in a planar shape, on which a pixel electrode havinga slit is provided with an insulating film interposed therebetween, torotate liquid crystal molecules by the electric field generated betweenthe pixel electrode and the common electrode. This type can increase thelight transmittance, and is now a mainstream IPS mode. An organicpassivation film is used for flattening the base on which the commonelectrode is formed. However, the organic passivation film is highlyhygroscopic and absorbs water from the air when it is left outside.Then, in the film formation, the water absorbed by the organicpassivation film is released during heat treatment. This affects thefilm formed on the organic passivation film, causing it to peel off.

As a method to solve such a problem, JP-A No. 271103/2009 describes aconfiguration in which an interlayer insulating film is formed on anorganic passivation film on an image signal line, and a through hole isformed along the image signal line in the interlayer insulating film toallow gas present in the organic passivation film to be released fromthe through hole. Further, in JP-A No. 271103/2009, the through hole iscovered by a transparent electrode that is electrically connected to thecommon electrode.

In order to describe the problem in the related art, first thecross-sectional structure of an IPS liquid crystal display device willbe described. FIG. 9 is a cross-sectional view showing the structure ofa pixel portion of a display area 10 of the liquid crystal displaydevice. Note that the cross-sectional view of FIG. 9 is an example ofthe basic structure, and does not correspond one-to-one to the figuressuch as FIG. 2 which is a top view of an embodiment of the presentinvention described below. As shown in FIG. 9, the liquid crystaldisplay device to which the present invention is applied is a top-gateTFT using poly-Si for a semiconductor layer 103. In FIG. 9, a first basefilm 101 of SiN and a second base film 102 of SiO₂ are formed on a glasssubstrate 100 by chemical vapor deposition (CVD). The role of the firstbase film 101 and the second base film 102 is to prevent thesemiconductor layer 103 from being contaminated with impurities from theglass substrate 100.

The semiconductor layer 103 is formed on the second base film 102. Inorder to form the semiconductor layer 103, a-Si film is formed on thesecond base film 102 by CVD, which is then converted into poly-Si filmby laser annealing. Then, the poly-Si film is patterned byphotolithography.

A gate insulating film 104 is formed on the semiconductor film. The gateinsulating film 104 is SiO₂ film derived from tetraethyl orthosilicate(TEOS). This film is also formed by CVD. Then, a gate electrode 105 isformed on the gate insulating film 104. The gate electrode 105 is formedon the same layer as a scan signal 30 at the same time. For example, thegate electrode 105 is formed from MoW film. When it is necessary toreduce the resistance of the scan line 30, Al alloy is used.

The gate electrode 105 is patterned by photolithography. At the time ofpatterning, impurities such as phosphor or boron are doped in thepoly-Si layer to form a source S or drain D in the poly-Si layer.Further, a lightly doped drain (LDD) layer is formed between a channellayer of the poly-Si layer, and the source S or drain D by using thephotoresist in patterning the gate electrode 105.

Then, a first interlayer insulating film 106 is formed of SiO₂ so as tocover the gate electrode 105. The role of the first interlayerinsulating film 106 is to provide electrical insulation between the gateline 105 and a source electrode 107. The source electrode 107 is formedon the first interlayer insulating film 106. The source electrode 107 isconnected to the pixel electrode 112 through a contact hole 130. In FIG.9, the source electrode 107 is made wide enough to cover the TFT. Thedrain D of the TFT is connected to the image signal line at a point notshown.

The source electrode 107 is formed on the same layer as the image signalline at the same time. In order to reduce the resistance, AlSi alloy isused for the source electrode 107 or the image signal line. In the AlSialloy, hillock formation occurs or Al diffuses into other layers. Inorder to prevent such a phenomenon, AlSi is sandwiched by a barrierlayer of MoW and a cap layer. Alternatively, Mow or MoCr may be usedinstead of using Al.

The source electrode 107 and the source S of the TFT are connected toeach other through the contact hole 130 formed in the gate insulatingfilm 104 and the first interlayer insulating film 106. An inorganicpassivation film 108 is formed and covers the source electrode 107 so asto protect the entire TFT. Similarly to the first base film 101, theinorganic passivation film 108 is formed by CVD.

An organic passivation film 109 is formed so as to cover the inorganicpassivation film 108. The organic passivation film 109 is formed of aphotosensitive acrylic resin. Examples of the material of the organicpassivation film, in addition to the acrylic resin, are a siliconeresin, epoxy resin, and polyimide resin. The organic passivation film109, which has a role of a flattening film, is made thick. The thicknessof the organic passivation film 109 is 1 to 4 μm, and in most cases,about 2 μm.

The contact hole 130 is formed in the inorganic passivation film 108 andin the organic passivation film 109 to provide electrical continuitybetween a pixel electrode 110 and the source electrode 107. Thephotosensitive resin used as the organic passivation film 109 is appliedand then exposed. In this way, only the portion exposed by light isdissolved with a specific developer. In other words, when thephotosensitive resin is used, the formation of photoresist can beomitted. After the contact hole is formed in the organic passivationfilm 109, the organic passivation film 109 is annealed at about 230° C.Thus, the organic passivation film 109 is completed. The organicpassivation film 109 is dry etched using the resist as a mask, in orderto form the contact hole in the inorganic passivation film 108. In thisway, the contact hole 130 is formed to provide electrical continuitybetween the source electrode 107 and the pixel electrode 110.

The top surface of the organic passivation film 109 formed as describedabove is flat. Amorphous indium-tin-oxide (ITO) is deposited bysputtering on the top of the organic passivation film 109, and thenpatterned using photoresist. Then, the ITO is etched by sulfuric acid topattern the common electrode 110. The common electrode 110 is formed ina planner shape, avoiding the contact hole 130. Then, the ITO ispolycrystallized by annealing at 230° C. in order to reduce theelectrical resistance. The common electrode 110 is formed of ITO whichis a transparent electrode. The thickness of the common electrode 110is, for example, 77 μm

Then, a second interlayer insulating film 111 is formed by CVD so as tocover the common electrode 110. At this time, the temperature conditionof CVD is about 230° C., which is called low temperature CVD. Then, thesecond interlayer insulating film 111 is patterned by photolithographyprocess. In FIG. 9, the second interlayer insulating film 111 does notcover the side wall of the contact hole 130. However, it is alsopossible that the second interlayer insulating film 111 covers the sidewall of the contact hole 130.

The other films, such as the first base film 101 and the inorganicpassivation film 108 are formed by CVD at a temperature of 300° C. ormore. In general, the higher the temperature at which a CVD film and thelike is formed the greater the adhesion to the base film. However, theorganic passivation film 109 has been formed below the second interlayerinsulating film 111. Thus, the characteristics of the organicpassivation film 109 may be changed when the temperature is 230° C. orhigher. For this reason, the second interlayer insulting film 111 isformed by low temperature CVD. When the second interlayer insulatingfilm 111 is formed by low temperature CVD, there is a problem with theadhesion of the organic passivation film 109 to the other film, inparticular to the common electrode 110 or the second interlayerinsulating film 111.

The pixel electrode 112 having a slit 115 is formed by sputtering theamorphous ITO on the second interlayer insulating film 111 through aphotolithography process. The pixel electrode 112 is connected to thesource electrode 107 through the contact hole 113. When a signal voltageis applied to the pixel electrode 112, electric field lines aregenerated between the common electrode 110 and the pixel electrode 112through the slit 115. The electric field rotates the liquid crystalmolecules 301, thereby controlling the transmittance of light from abacklight for each pixel to form an image. The pixel electrode 112 isformed of ITO which is a transparent conductive film. The thickness ofthe pixel electrode 112 is, for example, in the range of 40 nm to 70 nm.An oriented film 113 is formed so as to cover the pixel electrode 112.

A counter substrate 200 is provided with a liquid crystal layer 300interposed between the TFT substrate 100 and the counter substrate 200.A color filter 201 is formed within the counter substrate 200. The colorfilter 201 includes color filters of red, green, and blue in each pixelto form a color image. A black matrix 202 is formed between the colorfilters 201 to increase the contrast of the image. Note that the blackmatrix 202 also has a role as a light shielding film of the TFT toprevent the photocurrent from flowing into the TFT.

An overcoat film 203 is formed so as to cover the color filters 201 andthe black matrix 202. The surface of the color filters 201 and the blackmatrix 202 is rough. Thus, the surface is flattened by the overcoat film203. The oriented film 113 is formed on the overcoat film 203 for theinitial orientation of the liquid crystal molecules. Note that FIG. 2shows the case of the IPS, so that a counter electrode is formed on theside of the TFT substrate 100 but not on the side of the countersubstrate.

As shown in FIG. 9, in the case of the IPS, the conductive film is notformed inside the counter substrate 200. As a result, the potential ofthe counter substrate 200 becomes unstable. In addition, externalelectromagnetic noise enters the liquid crystal layer 300 and affectsthe image. These problems eliminate by forming an external conductivefilm 210 on the outside of the counter substrate 200. The externalconductive film 210 is formed by sputtering the ITO which is thetransparent conductive film.

As described above, the second interlayer insulating film formed on theorganic passivation film is deposited by low temperature CVD at about230° C. Thus, the adhesion of the second interlayer insulating film tothe base film is low. The organic passivation film, which is formedbelow the second interlayer insulating film, absorbs water from the airwhen it is left outside. Then, when the organic passivation film isannealed to form various films on the organic passivation film, thewater absorbed by the organic passivation film is released. At thistime, the second interlayer insulating film peels off due to its lowadhesion.

In order to solve the above problem, JP-A No. 271103/2009 describes aconfiguration in which a thin through hole is formed in the secondinterlayer insulating film and along the image signal line, so that thewater absorbed by the organic passivation film is let out from thethrough hole. Further, in JP-A No. 271103/2009, the through hole iscovered by the ITO film. The ITO film is electrically connected to thecommon electrode so as to have the shielding effect.

However, JP-A No. 271103/2009 has the following problem. That is, thesecond interlayer insulating film is formed by low temperature CVD, sothat the film structure is less precise than the film structure formedby high temperature CVD. Thus, when the contact hole is formed along theimage signal by etching, the width of the though hole is not stabilizedbecause of the unstable etching rate. As a result, the through hole isvery likely to reach the pixel electrode. When the through hole reachesthe pixel electrode, the disturbance of the electric field occurs inthis portion of the pixel electrode, in which the liquid crystalmolecules may not be controlled adequately. As a result, light leakageor other failure occurs. In addition, when the through hole is coveredby the ITO film electrically connected to the common electrode, thepixel electrode and the common electrode are electrically connected toeach other. As a result, the pixel is faulty.

Another problem of JP-A No. 271103/2009 is that when the through hole isformed in the second interlayer insulating film, its effect is reducedby covering the through hole formed along the image signal line by theITO. In other words, also when the pixel electrode of ITO is formed onthe second interlayer insulating film, the ITO film is annealed at 230°C. to reduce the resistance of the ITO. At the same time, the orientedfilm is also annealed to be imidized. Thus, the water absorbed by theorganic passivation film is released when the ITO and oriented films areformed. For this reason, it is necessary to effectively release thewater from the through hole formed in the second interlayer insulatingfilm.

SUMMARY OF THE INVENTION

The present invention is to solve the above problems, and to prevent thesecond insulating film from peeling off, without reducing the processlatitude and without degrading the image quality.

The present invention overcomes the above problems. Concrete steps areas follows. There is provided an IPS liquid crystal display device thatuses a top gate TFT as a switching element. The TFT uses poly-Si as asemiconductor layer. An inorganic passivation film and an organicpassivation film are formed so as to cover the TFT. A common electrodeis formed on the organic passivation film. An interlayer insulating filmis formed on the common electrode. Then, a pixel electrode having a slitis formed on the interlayer insulating film.

The width of an image signal line is wide in the vicinity of the TFT, inwhich the image signal line is electrically connected to the drain orsource portion of the TFT through a contact hole. In the wide portion ofthe image signal line, a through hole is formed in the interlayerinsulating film formed on the common electrode. In this way, gasgenerated in the organic passivation films is released from the throughhole. Because the through hole for gas release is formed in the wideportion of the image signal line, if the diameter of the through holevaries by etching, this will not affect the driving of the liquidcrystal molecules. Further, the diameter of the through hole for gasrelease is greater than the diameter of the contact hole for providingthe electrical connection between the image signal line and the sourceor drain portion. In addition, the through hole for gas release is notcovered by the conductive film such as ITO. Thus, it is possible toeffectively release the gas from the organic passivation film to theoutside.

The above configuration can also be applied to the IPS of the type inwhich the pixel electrode is formed on the organic passivation film, onwhich the interlayer insulating film is formed, and then the commonelectrode having a slit is formed on the interlayer insulating film.

Further, it is possible that the through hole for gas release is formedin the interlayer insulating film covering the peripheral circuit formedin the vicinity of the display area. Or it is also possible to form thethrough hole for gas release in the interlayer insulating film coveringthe portion in which a testing element group (TEG) pattern or analignment mark is formed in the vicinity of the terminal portion of theTFT substrate.

According to the present invention, it is possible to prevent theinterlayer insulating film from peeling off. As a result, the productionyield of the liquid crystal display device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a liquid crystal display device;

FIG. 2 is a top view of a pixel portion according to a first embodimentof the present invention;

FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2;

FIG. 4 is a cross-sectional view according to a second embodiment of thepresent invention;

FIG. 5 is a top view showing an example in which the present inventionis applied to the TEG pattern portion;

FIG. 6 is a cross-sectional view taken along line B-B in FIG. 5;

FIG. 7 is a top view showing an example in which the present inventionis applied to the alignment mark portion;

FIG. 8 is a cross-sectional view taken along line C-C in FIG. 7; and

FIG. 9 is a cross-sectional view of the display area of the liquidcrystal display device having a top-gate type TFT.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail withreference to embodiments.

First Embodiment

FIG. 1 is a top view of a small liquid crystal display device used forportable electronic devices such as mobile phones, which is an exampleof the product to which the present invention is applied. In FIG. 1, acounter substrate 200 is provided on a TFT substrate 100. Although notshown, there is a liquid crystal layer interposed between the TFTsubstrate 100 and the counter substrate 200. The TFT substrate 100 andthe counter substrate 200 are bonded together by a sealing material 20formed around the frame. In FIG. 1, liquid crystal is injected betweenthe substrates by a dropping method, so that no injection hole isformed.

The TFT substrate 100 is formed larger than the counter substrate 200.In a portion of the TFT substrate 100 extending beyond the countersubstrate 200, a terminal portion 150 is formed to supply power, imagesignals, scan signals, and the like, to a liquid crystal cell 1.Further, on the outside of the terminal portion 150, there is formed atesting element group (TEG) used in the test of the circuitcharacteristics, or an alignment mark used in the alignment of the upperand lower boards in the production process.

FIG. 2 is a top view of the structure of a part of the pixel portion inthe display area 10 shown in FIG. 1. In FIG. 2, the pixel electrode 112having the slit 115 is formed in an area surrounded by an image signalline 40 and a scan line 30. A common electrode, not shown, is formedbelow the pixel electrode 112 through a second interlayer insulatingfilm not shown. An image signal is supplied to the pixel electrode 112from the image signal line 40 through TFT.

In FIG. 2, a first TFT and a second TFT are arranged in series from theimage signal line 40 to the pixel electrode 112. In FIG. 2, a contacthole 130 is formed in a wide portion of the image signal line 40 toconnect the semiconductor layer 103 with the image signal line 40. Thesemiconductor layer 103 extends beyond the scan line 30, and is foldedacross the scan line 30 once again to connect to the pixel electrode112.

The semiconductor layer 103 includes a channel portion below the scanline 30 having a role as a gate electrode, in which a drain portion or asource portion is formed on either of the two sides of the scan line 30.In FIG. 2, for convenience, the side near the image signal line 40 iscalled the drain portion and the side near the pixel electrode 112 iscalled the source portion in each TFT. In other words, in the first TFT,the side connected to the image signal line 40 is the drain portion, andthe side connected to the second TFT is the source portion, while in thesecond TFT, the side connected to the first TFT is the drain portion,and the side connected to the pixel electrode 112 is the source portion.

In FIG. 2, the scan line 30 also functions as the gate electrode. Thechannel portion of the semiconductor layer 103 is formed below the scanline 30. Thus, in FIG. 2, two TFTs are present between the image signalline 40 and the pixel electrode 112. In FIG. 2, a through hole 140 isalso formed in the contact portion of the image signal line 40 and thesemiconductor layer 103. The area of the through hole is greater thanthe area of the contact hole 130. The through hole 140 is used torelease gas from an organic passivation film 109 not shown in FIG. 2.

In the counter substrate 200, there is formed a black matrix in the areashown in FIG. 2. The black matrix covers the image signal line 40, thescan line 30, the through hole 140, the contact hole 130, the channelportion of the TFT, and the like, formed on the TFT substrate 100 asdescribed above.

FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2. Thesemiconductor layer 103 is formed on the first base film and on thesecond base film. A gate insulating film 104 and a first interlayerinsulating film 106 are formed so as to cover the semiconductor layer103, on which the image signal line 40 is formed. The image signal line40 is connected to the semiconductor layer 103 through the contact hole130 that is formed in the gate insulating film 104 and in the firstinterlayer insulating film 106. The inorganic passivation film 108 isformed so as to cover the image signal line 40 or the first interlayerinsulating film 106. Then, the organic passivation film 109 is formed onthe inorganic passivation film 108.

A common electrode 110 is formed on the organic passivation film 109.Then, a second interlayer insulating film 111 is formed on the commonelectrode 110. The second interlayer insulating film 111 provideselectrical insulation between the common electrode 110 and the pixelelectrode 112. However, the pixel electrode 112 is not present on theimage signal line 40. In the present invention, the through hole 140 isformed in this area of the second interlayer insulating film 111 to beable to easily release water and the like absorbed by the organicpassivation film 109. Note that the oriented film is omitted in FIG. 3.

As shown in FIGS. 2 and 3, the diameter of the through hole 140 isgrater than the diameter of the contact hole 130. This is in order toeffectively release the gas absorbed by the organic passivation film109. The portion in which the contact hole 130 is formed has a concaveshape, so that peeling of the second interlayer insulating film 111 ismore likely to occur. For this reason, it is effective to form thethrough hole 140 for gas release in this area.

As shown in FIG. 2, the portion in which the through hole 140 for gasrelease is formed is the wide portion of the image signal line 40, whichalso functions as a light shielding electrode 135. Thus, if adisturbance in the orientation of the liquid crystal molecules occursdue to the influence of the through hole 140 for gas release, lightleakage will not occur in this portion.

The through hole 140 for gas release is formed by etching. The secondinterlayer insulating film 111 is formed by low temperature CVD, so thatthe dimension control in etching is more difficult than the case of thefilm formed by high temperature CVD. However, as shown in FIG. 2, thelight shielding electrode 135 having a large area is formed below thethrough hole 140 for gas release. Thus, light leakage will not occur ifthe dimension of the through hole 140 for gas release varies.

Further, in FIG. 2, the through hole 140 for gas release is formed veryclose to the scan line 30. In the counter substrate 200, the blackmatrix 202 is formed in the portion corresponding to the scan line 30.Thus, even if light leakage occurs due to the influence of the throughhole 140 for gas release, the light can also be blocked by the blackmatrix 202.

As described above, according to the present invention, the through hole140 for gas release is formed in the vicinity of the scan line 30 and inthe wide portion of the image signal line 40. Thus, it is possible toprevent peeling of the second interlayer insulating film 111. Further,the wide portion of the image signal line 40 also functions as the lightshielding electrode 135, preventing side effects such as light leakagedue to the formation of the through hole 140 for gas release.

Note that in the present invention, the through hole 140 for gas releaseformed in the second interlayer insulating film 111 is not covered byITO. As a result, it is possible to release gas from the organicpassivation film to the outside more effectively.

Second Embodiment

In an upper wiring circuit 160 corresponding to the shaded part abovethe display area 10 shown in FIG. 1, a portion of protective wiringcircuits or drive circuits is formed. These protective circuits have aTFT. The inorganic passivation film 108 and the organic passivation film109 are formed so as to cover the TFT, on which the common electrode 110is formed. Then, the second interlayer insulating film 111 is formed soas to cover the common electrode 110. There is also a problem with theadhesion of the second interlayer insulating film 111, similar to thecase of the display area 10 described in the first embodiment.

FIG. 4 is a cross-sectional view in the area in which the protectivecircuit and the like are formed. FIG. 4 is a view of the cross sectionincluding TFT. FIG. 4 is the same as that described with reference toFIG. 9, and so the details will be omitted here. In FIG. 4, the sourceelectrode 107 or drain electrode is connected through the contact hole130 formed in the gate insulating film 104 and in the first interlayerinsulating film 106, both of which cover the semiconductor layer 103.The source electrode 107 or drain electrode is the line formed in thesame layer as the image signal line 40. The inorganic passivation film108 is formed so as to cover the source electrode 107 or drainelectrode. Then, the organic passivation film 109 is formed on theinorganic passivation film 108.

On the inorganic passivation film 108, there is an electrode of ITOformed at the same time as the common electrode 110. This electrode iselectrically connected to the common electrode 110, and will also bereferred to as the common electrode 110. This common electrode 110 doesnot drive the liquid crystal molecules as in the case of FIG. 9, whichserves as a simple connection line or a shield electrode. The secondinterlayer insulating film 111 is formed so as to cover the commonelectrode 110. The contact hole 130 is formed in the vicinity of theTFT, in which the adhesion of the second interlayer insulating film 111is particularly low. Thus, the through hole 140 is formed in thecorresponding portion of the second interlayer insulating film 111 torelease gas from the organic passivation film 109.

In FIG. 4, the through hole 140 for gas release is formed on the outsideof the display area 10, so that light leakage or other problems will notoccur if the dimension of the through hole 140 for gas release somewhatvaries. Thus, a relatively larger through hole can be made on theoutside of the display area 10 than inside. As a result, it is possibleto prevent peeling of the second interlayer insulating film 111 moresurely. Note that also in this embodiment, the through hole 140 for gasrelease formed in the second interlayer insulating film 111 is notcovered by ITO. Thus, it is possible to release gas from the organicpassivation film to the outside more effectively.

Third Embodiment

In the liquid crystal display device to which the present invention isapplied, the TFT is formed of poly-Si, in which a drive circuit can bemounted within the liquid crystal display panel. When the drive circuitis formed within the liquid crystal display panel, it is necessary tocheck the change in the circuit characteristics during the process. Forthis reason, as shown in FIG. 1, a testing element group (TEG) 170 isformed on the outside of the terminal portion 150. The characteristicsof the TFT and the like are checked by the TEG 170. Thus, the TEG 170should also have the same structure as the display area 10 or the drivecircuit portion.

Also in the TEG 170, the common electrode 110 of ITO is formed on theorganic passivation film 109. Then, the second interlayer insulatingfilm 111 is present on the common electrode 110. This is the same as inthe display area 10 and the like. FIG. 5 is an example of the TEG 170,in which a long resistance is formed between terminals 1501 and 1502 tomeasure the resistance formed by the common electrode 110. Although notshown, the second interlayer insulating film 111 is formed on this longresistance. The common electrode 110 is formed on the organicpassivation film 109. When the water is released from the organicpassivation film 109, the second interlayer insulating film 111 peelsoff, and it is no longer able to function as the TEG 170. In thisembodiment, as shown in FIG. 5, a large number of rectangular throughholes 140 for gas release are formed to allow gas to be easily releasedfrom the organic passivation film 109. In this way, the secondinsulating film 111 is prevented from peeling off.

FIG. 6 is a cross-sectional view taken along line B-B in FIG. 5. Thefirst and second base films are omitted in FIG. 6. FIG. 6 shows that thesemiconductor layer 103, the gate insulating film 104, the firstinterlayer insulating film 106, the inorganic passivation film 108, andthe organic passivation film 109 are laminated in this order from thebottom. Then, the common electrode 110 is formed on the organicpassivation film 109. The second interlayer insulating film 111 isformed on the common electrode 110. The through holes 140 for gasrelease are formed in the second interlayer insulating film 111, inorder that the water and the like can be easily released from theorganic passivation film 109. As a result, the second interlayerinsulating film 111 is prevented from peeling off.

The manufacturing process of liquid crystal display devices is asfollows. A mother board is formed by bonding a mother TFT board in whicha large number of the TFT substrates 100 are formed, to a mother counterboard in which a large number of the counter substrates 200 are formed.Then, individual liquid crystal display panels are cut out of the motherboard by scribing or other method. When the mother TFT substrate and themother counter substrate are bonded together by a sealing material, itis necessary to use the alignment mark 180.

FIG. 7 is an example of an alignment mark 180. In FIG. 7, the alignmentmark 180 is formed by combining square units. The rectangular throughholes 140 for gas release are present in some of the units of thealignment mark 180. The through holes 140 are formed in the secondinterlayer insulating film 111. The through holes 140 for gas releaseallow the water and the like absorbed by the organic passivation film109 to be easily released. As a result, the second interlayer insulatingfilm 111 is prevented from peeling off.

FIG. 8 is a cross-sectional view taken along line C-C in FIG. 7. Theconfiguration of FIG. 8 is the same as that described with reference toFIG. 6, except that the semiconductor layer 103 is not present. Thus,the description thereof will be omitted. Note that FIG. 6 or FIG. 8 isan example of the cross section. It does not necessarily mean that thesemiconductor layer 103 is typically present in FIG. 6, and that thesemiconductor layer 103 is typically not present in FIG. 8.

As described above, when the organic passivation film 109 and the secondinterlayer insulating film 111 are also formed in the area other thanthe area in which the liquid crystal is injected in the liquid crystaldisplay panel, the through holes 140 for gas release are also formed inthis area of the second interlayer insulating film 111, to be able tofunction as the TEG 170 or the alignment mark 180 without fail. However,the TEG 170 or the alignment mark 180 shown in FIG. 1 is not used afterthe liquid crystal display device is completed. Thus, the portion of theTEG 170 or the alignment mark 180 is often removed in the scribingprocess. Note that also in this embodiment, the through hole 140 for gasrelease formed in the second interlayer insulating film is not coveredby ITO. Thus, it is possible to release gas from the organic passivationfilm to the outside more effectively.

In the above examples, the IPS is the type in which the common electrode110 is formed on the organic passivation film 109, on which the pixelelectrode 112 having the slit 115 is formed through the secondinterlayer insulating film 111. However, the present invention can alsobe applied in the same way to the other types of IPS in which the pixelelectrode 112 is formed on the organic passivation film 109, on whichthe common electrode having the slit 115 is provided through theinterlayer insulating film 111.

What is claimed is:
 1. A liquid crystal display device comprising apixel electrode in an area surrounded by scan lines extending in a firstdirection and arranged in a second direction and by image signal linesextending in the second direction and arranged in the first direction,wherein the pixel electrode is supplied with an image signal from theimage signal line through a TFT, wherein the TFT includes asemiconductor layer having a channel portion, a drain portion formed onthe side of the image signal line, and a source portion formed on theside of the pixel electrode, wherein a gate insulating film is formed soas to cover the semiconductor layer, wherein a gate electrode is formedon the gate insulating film above the channel portion, wherein a firstinterlayer insulating film is formed so as to cover the gate electrode,wherein the image signal line is provided on the first interlayerinsulating film, wherein an organic film is formed to cover the imagesignal line, wherein a common electrode, which is a transparentelectrode, is formed on the organic film, wherein a second interlayerinsulating film is formed on the common electrode, wherein the pixelelectrode, which is a transparent electrode, having a slit is formed onthe second interlayer insulating film, wherein a portion of the imagesignal line connected to the drain portion of the TFT has a width whichis greater than a width of an other portion of the image signal line,wherein the image signal line is connected in the greater width portionto the drain portion through a contact hole, wherein a through hole isformed in the second interlayer insulating film in the greater widthportion of the image signal line, and wherein the diameter of thethrough hole is greater than the diameter of the contact hole.
 2. Theliquid crystal display device according to claim 1, wherein the TFTincludes a first TFT and a second TFT, wherein the first TFT has a drainportion connected to the image signal line, wherein the second TFT isconnected to the first TFT and has a source portion connected to thepixel electrode, and wherein the scan line also functions as the gateelectrodes of the first TFT and the second TFT.
 3. The liquid crystaldisplay device according to claim 1, wherein the through hole formed inthe second interlayer insulating film is not covered by the transparentelectrode.
 4. A liquid crystal display device comprising a pixelelectrode formed in an area surrounded by scan lines extending in afirst direction and arranged in a second direction and by image signallines extending in the second direction and arranged in the firstdirection, wherein the pixel electrode is supplied with an image signalfrom the image signal line through a TFT, wherein the TFT includes asemiconductor layer having a channel portion, a drain portion formed onthe side of the image signal line, and a source portion formed on theside of the pixel electrode, wherein a gate insulating film is formed soas to cover the semiconductor layer, wherein a gate electrode is formedon the gate insulating film above the channel portion, wherein a firstinterlayer insulating film is formed so as to cover the gate electrode,wherein the image signal line is provided on the first interlayerinsulating film, wherein an organic film is formed to cover the imagesignal line, wherein the pixel electrode, which is a transparentelectrode, is formed on the organic film, wherein a second interlayerinsulating film is formed on the pixel electrode, wherein a commonelectrode, which is a transparent electrode, having a slit is formed onthe second interlayer insulating film, wherein a portion of the imagesignal line connected to the drain portion of the TFT has a width whichis greater than a width of an other portion of the image signal line,wherein the image signal line is connected in the greater width portionto the drain portion through a contact hole, wherein a through hole isformed in the second interlayer insulating film in the greater widthportion of the image signal line, and wherein the diameter of thethrough hole is greater than the diameter of the contact hole.
 5. Theliquid crystal display device according to claim 4, wherein the TFTincludes a first TFT and a second TFT, wherein the first TFT has a drainportion connected to the image signal line, wherein the second TFT isconnected to the first TFT and has a source portion connected to thepixel electrode, and wherein the scan line also functions as the gateelectrodes of the first TFT and the second TFT.
 6. The liquid crystaldisplay device according to claim 4, wherein the through hole formed inthe second interlayer insulating film is not covered by the transparentelectrode.
 7. A liquid crystal display device comprising a display areaand a peripheral circuit portion, wherein the peripheral circuit portionincludes a TFT including a semiconductor layer having a channel portion,a source portion, and a drain portion, wherein a gate insulating film isformed so as to cover the semiconductor layer, wherein a gate electrodeis formed on the gate insulating film above the channel portion, whereina first interlayer insulating film is formed so as to cover the gateelectrode, wherein a metal line is formed on the first interlayerinsulating film, wherein the metal line is connected to the drainportion or the source portion through a contact hole formed in the firstinterlayer insulating film and in the gate insulating film, wherein anorganic film is formed to cover the metal line, wherein a line of ITO isformed on the organic film, wherein a second interlayer insulting filmis formed on the ITO line, wherein a through hole is formed in thesecond interlayer insulating film, and wherein the diameter of thethrough hole is greater than the diameter of the contact hole.
 8. Theliquid crystal display device according to claim 7, wherein the throughhole formed in the second interlayer insulating film is not covered byITO.
 9. A liquid crystal display device comprising a TFT substrate and acounter substrate, wherein the TFT substrate and the counter substrateare bonded face-to-face with a liquid crystal layer formed inside,wherein a terminal portion and an alignment mark are formed in a portionof the TFT substrate not facing the counter substrate, wherein thealignment mark is configured such that a gate insulating film, a firstinterlayer insulating film, and an organic film are laminated in thisorder on the TFT substrate, wherein a transparent electrode is formed onthe organic film, wherein a second interlayer insulating film is formedon the transparent electrode, and wherein a through hole is formed inthe second interlayer insulating film in an area in which the alignmentmark is formed.
 10. The liquid crystal display device according to claim9, wherein the through hole formed in the second interlayer insulatingfilm is not covered by the transparent electrode.